Abnormal growth of fibroblasts are involved in hypertrophic scars formed after injury, and various diseases such as pulmonary fibrosis, cirrhosis and nephrosclerosis. It is said that TGF-β is involved in processes that induce these abnormal growth (see, for example, Patent Document 1, Patent Document 2 and Patent Document 3). However, since TGF-β is a multi-task biological substance, treatment of these diseases by simple suppression of TGF-β has been difficult in many aspects, and it is thought that such a fact is preventing development of an effective TGF-β inhibitor having only small side effects. That is, it is thought that discovery and selective suppression of factors positioned downstream of TGF-β, which factors are responsible for the abnormal growth of fibroblasts directly involved in these diseases, may be an effective means for suppressing the abnormal growth of fibroblasts.
On the other hand, although ETFB is a protein involved in electron transfer (see, for example, Patent Document 4, Patent Document 5, Patent Document 6 and Patent Document 7) and sometimes used as a biomarker, its functions are hardly known. It is reported, for example, that a mutation of ETFB is found in lipid storage myopathy (see, for example, Non-patent Document 1), that ETFB may be a factor involved in type II diabetes (see, for example, Non-patent Document 2), and that ETFB may be a factor involved in multiple acyl-CoA dehydrogenase deficiency (MADD) (see, for example, Non-patent Document 3). However, no function of ETFB is known at all for the skin or fibroblasts. Further, no relationship between ETFB and TGF-β is known.
On the other hand, it has already been reported that, when fibroblasts are cultured under tension in a collagen gel, promoted cell growth, increased expression levels of collagen and the like, and phenomena similar to those observed in fibrosis can observed, and that, in cases where this culture is carried out in the presence of TGF-β, differentiation of fibroblasts into myofibroblasts can be observed (see, for example, Non-patent Document 4). However, no factor for the cell growth in such a phenomenon has been clarified.